AW: [PATCH 07/12] kern_tc.c: Remove verification of th_generation for pps functions

[Gabriel.Moyano at dlr.de]

> On 07/04/2022 10:36, Gabriel Moyano wrote:
> > ---
> >   cpukit/score/src/kern_tc.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > diff --git a/cpukit/score/src/kern_tc.c b/cpukit/score/src/kern_tc.c
> > index a5c7b4b841..a8ba268ea3 100644
> > --- a/cpukit/score/src/kern_tc.c
> > +++ b/cpukit/score/src/kern_tc.c
> > @@ -2109,9 +2109,11 @@ pps_capture(struct pps_state *pps)
> >   	pps->capffth = fftimehands;
> >   #endif
> >   	pps->capcount = th->th_counter->tc_get_timecount(th->th_counter);
> > +#ifndef __rtems__
> >   	atomic_thread_fence_acq();
> >   	if (pps->capgen != th->th_generation)
> >   		pps->capgen = 0;
> > +#endif /* __rtems__ */
> >   }
> >
> >   void
> > @@ -2135,10 +2137,12 @@ pps_event(struct pps_state *pps, int event)
> >   	/* Nothing to do if not currently set to capture this event type. */
> >   	if ((event & pps->ppsparam.mode) == 0)
> >   		return;
> > +#ifndef __rtems__
> >   	/* If the timecounter was wound up underneath us, bail out. */
> >   	if (pps->capgen == 0 || pps->capgen !=
> >   	    atomic_load_acq_int(&pps->capth->th_generation))
> >   		return;
> > +#endif /* __rtems__ */
> >
> >   	/* Things would be easier with arrays. */
> >   	if (event == PPS_CAPTUREASSERT) {
> > @@ -2189,10 +2193,12 @@ pps_event(struct pps_state *pps, int event)
> >   	bintime_addx(&bt, pps->capth->th_scale * tcount);
> >   	bintime2timespec(&bt, &ts);
> >
> > +#ifndef __rtems__
> >   	/* If the timecounter was wound up underneath us, bail out. */
> >   	atomic_thread_fence_acq();
> >   	if (pps->capgen != pps->capth->th_generation)
> >   		return;
> > +#endif /* __rtems__ */
> >
> >   	*pcount = pps->capcount;
> >   	(*pseq)++;
> 
> Why is this change justified?

Since only one timehands object is used, the generation is updated more frequently. This can even happen between pps_capture() and pps_event(), making the synchronization impossible.